Concrete walls and concrete structures are often associated with hardness and coldness. However, with the change of sunshine, concrete walls give some changes of impression. The psychological measurements with nine seven-rated-scales were conducted for nine architectural concrete specimens with variety of surface finishing under the various conditions of sunshine. We measured the illuminance and the color of the surface of concrete specimens with various sunshine conditions. The results are as follows : People are impressed as warm by the high illuminance of the vertical plane or by taking on a red tinge of sun light, and impressed as cold by the low illuminance of the vertical plane. People are impressed as abundant, light and soft by the change of incident angle of sun light, and impressed as poor, heavy, and hard by the low illuminance of the vertical plane.
The aim of this paper is to obtain a better understanding of the process of chloride intrusion into hardened concrete exposed to the various zones in marine environments. Chloride content in the concrete is one of the main factors that dictate the initiation, magnitude and rate of steel corrosion inconcrete. Although extensive data are available on the chloride content in hardened concrete under various marine environments, they are scattered in literature, the variable involved are many and there is nounifying approach to correlate this information and formulate a rational basis to explain how the process of chloride contamination develops under marine environments. This research work is the initial stage of a long term study to provide a realistic mathematical model for chloride intrusion into concrete exposed to real environments.
For the purpose with apllying steel fiber reinforced concrete (SFRC) to structural components, it is an important subject to establish and connect each other designs of mix proportion, material characteristics and component section, respectively for good workability, necessary mechanical properties and required component performance of SFRC. In this paper, in order to establish a material design of SFRC, experimental investigations were conducted by compression, tension and fracture toughness testings for a sines of SFRC specimens with manufactured under various mix proportions. From the experimental results, quantitative analyses were performed concerning interactions among aspect ratio of steel fiber, fiber volume fraction and cement-water ratio on mechanical parameters of SFRC.
To properly evaluate watertightness of field concrete is extremely important from the standpoint of design and construction of watertight structures. In this research, permeability tests are performedon small standard specimens and cores sampled from field concrete with the purpose of seeking a method of evaluatingwatertightness of field concrete from the watertightness test values of small standard specimens of concrete used for evaluation of watertightness of field concrete, and comparison studies are made of the relations of the watertightness of the two. As a result, it is found that watertightness of field concrete are more reductions than small standard specimens.
In order to establish a practical design concept of the multilayered resin materials for repair of deteriorated concrete structures, it is important to evaluate the mechanical behaviors of interface among layers and concrete surface during various stages under service conditions as well as providing adequate chemically and physically stable bonding between them. The aim of this particular research is not only to develop a few indexes which represent their mechanical behaviors based on 2-D FEM analysis which considered the linear elastic fracture mechanics, but also to demonstrate the feasibility of applying the proposed indexes to optimum design of multilayered resin materials for repair of deteriorated concrete structures.
The theory to estimate amount of frozen water in cement paste was studied based on properties of electrolyte solution. A method to estimate amount of frozen water as a function of resistivity and temperature was proposed. Resistivity and temperature in cement paste with different moisture contents equilibrating to various relative humidity were measured in the temperature range from 20 to-45 C. Pore structure was measured by mercury penetration and adsorption. Conclusion is shown below. Moisture contents below approximately 3.5 monolayers is not freezable. The freezing point depends on supercooling and depression of melting point corresponding to pore radius. Few frozen water was observed below RH 90 % in the temperature range of freezing and thawing test (ASTM C 666). Water in the capillary pore larger than 100-150 λ is freezable in the temperature range of freezing and thawing test (ASTM C 666).
This study is carried out to clarify the influence of particleshape of fine aggregate to the properties of mortar in dam concrete. We use 8 kinds of fine aggregates. One of them is produced by cone crusher, three of them by Los Angeles machine with ceramic balls, one of them by rod mill and three of them by Barmax. Solid volume percentage for shape determination of the used fine aggregate ranges from 53.1% to 59.2%. In this experiment, moderate heat portland cement blended with 30% fly ash is used. This kind of cement is usually used in darn concrete. The ratio of fine aggregate to cementaneous material is 2 to 1, and Water to cementaneous material ranges from 0.33 to 0.48. The flow value, bleeding ratio and compressive strength of mortar are measured. The surface of the particle is observed by electron microscope. The surfaces of crushed sand stone and river sand are also observed to compare with granite aggregate. Results indicate that increase of solid volume percentage for shape determination by 1% has an equivalent effect of the increase of flow value by 10 mm. This means that the water content can be reduced by 4 to 5 kg/m‹SUP›3‹/SUP›.
This study is aimed to develope the practical design method of the multi-story precast reinforced concrete shear walls which have precast panels in cast-in-place frames. In this paper, the first, the estimating method of the shear capacity based on the shear resistance mechanism is explained. Next, it is shown that the existence of new failure modes which were not observed in cases of cast-in-place shear walls are found from past studies. The last, the appropriateness of the proposed mechanism model is demonstrated from viewpoints of the maximum shear capacity and the monolithic structure by past experimental results, and a design method is proposed.
This study was conducted to solve the technical problem for utilizing recycled concrete aggregate of nuclear power facilities. Waste concrete was crushed by using three kinds of crushers with different crushing mechanism followed by Jaw crusher's prior crushing. Test results of these crushed aggregate showed that the type of crusher and the number of crushing process did not affect the properties of crushed aggregate. Though recycled concrete showed relatively lower mechanical properties than conventional concrete, the difference was confirmed to be so slight to apply for practical use. As for durability of the concrete, recycled concrete has sufficient resistance to freezing and thawing, watertightness and less carbonation. However, higher drying shrinkage than conventional concrete was considered to take some countermeasure to reduce cracking of concrete. Development of curshing mechanism of recycled aggregate and method for reducing drying shrinkage of recycled concrete were proposed by the results of the study.
In the manufacture of soil-cement concrete using cement, soil and sand, precise control of the amount of water which assure the designed strength must be based on a consistent relationship of strength-water cement ratio supported by the concept of the effective water. We developed a new testing method, the drying acceleration method, that can estimate the saturated surface-dry state of soils, which forms the base of the concept of the effective water. Sample soils were taken from ten different construction sites over Japan, and four type of sand and one kaolin were used. Apparent saturated surface-dry state of these sample soils and sands were defined by this method. Our findings can be summarized as follows, (1) The apparent saturated surface?dry state do exist for soils. (2) The apparent saturated surface?dry state can be determined by the drying acceleration method. (3) The drying acceleration method may be favorably executed when the size of soil specimen is 5 mm under a drying condition of temperature at 40°C and relative humidity of 40% with an interval of measurement 60 minutes for soils and 10 minutes for sands.
In this paper, the basic properties of concrete containing the non?chloride and non-alkali type antifreezing admixtures, such as freezing point, setting, hardening and frost resistance at early ages were studied, and the utilization method of these admixtures to protect fresh concrete against frost damage in cold weather concreting was investigated. It was found that the freezing point of antifreeze concrete was-2°C to-4°C. The setting time at low temperature and the strength gains at early ages were accelerated by using antifreezers. The benefit of using antifreezers was not only the protection of fresh concrete against frost damage by lowering the freezing point but also the accelerative effect on the setting and hardening of the concrete. The relationship between the concentration of antifreezers and the allowable ambient temperature was derived from the results of the experimental and analytical studies. This is useful for assessment of effectiveness level of the antifreezers when used in cold weather concreting.
Color of concrete structure is different between at dry and wet surface conditions. For designing, it is very important to find how change peoples impressions by it. Ten architectural concrete specimens of nine hundred mm square with a variety of surface finishing were psychologically measured both at dry and wet surface conditions. Color and gloss were mechanically measured at these conditions. The results are as follows. The changes of psychological values due to wetting for smooth or hard concrete surface finishing, correlate closely with the change of color. Those for designed concrete finishing depend on the surface texture. Concrete with the glossy and light surface at dry condition, and concrete with glossy and warm surface at wet condition is felt comfortable.
The authors have been studying the relationships between properties of surface texture on concrete manufactures commonly used in concrete structures and sensory evaluation results, in order to establish reasonable landscape design methods of concrete structures. In the case of discussing about landscape of structures, not only the surface properties of concrete manufactures but also the distance from viewpoint to structures and the background formed structures have direct effects upon the landscape evaluation results.
A non-destructive testing method of concrete using impact acoustics induced by hammering on the surface of concrete structures was studied in this paper. The impact acoustics, which has strong relation with the vibration of concrete surface, can offer important information about the properties and the defects of the concrete structures. However the study related to this method has not been done sufficiently, although it is often used in the inspection of concrete structures. The relation between impact acoustics emitted from the surface of the concrete and the vibration at the same surface of the concrete was observed experimentally. Then some basic experiments were carried out to clarify the influence of defects like cracks and delaminations on amplitude and resonant frequency of impact acoustics. These experimental results are compared with the results of FEM analysis. And flow chart for judging the existence of flaws are also proposed in this paper.
According to the result investigated on the pore structure of portland cement cured under high temperature at early ages, it can be induced that compared to the case cured under 20°C condition, the proportion of larger pores in the case cured under high temperature increased obviously. The compressive strength of the case cured under high temperature was found to have a reverse relationship with the amount of the pores whose radii are larger than 10 nm. In addition, as the results indicated, with the increase on the compressive strength of hardened pastes cured under high temperature, the reverse relationship existing between the curing temperature and amount of pores whose radii are less than 10 nm become more apparent. Based on the above observation, the pores whose radii are less than 10 nm distribute more sparsely in the cured under high temperature than under 20°C condition.
In this paper, the size effect of shear capacity of concrete beams reinforced with FRP rods without stirrups is analyzed using the developed fictitious crack model based on fracture mechanics. The numerical analysis is performed for the case of different reinforcement stiffnessEs, 2.0×106, 1.0×106 and 6.7×105 kgf/cm2, and for different beam depth 10, 20, 50,100,200 and 300 cm.The result shows that the shear capacity declines with a decrease of reinforcement stiffness and the tendency of size effect of a beam reinforced with FRP is similar to that reinforced with normal steel bers
This study was executed to investigate the restrained stress development at early ages in axially restrained concrete prisms. It was cleared from the test results that the high tensile restraint stress was developed at an early age in high-strength concrete and that the inherent high tensile strength might not be utilized for the structural performance of high strength concrete members. An analytic calculation considering creep under varying stress and the time-dependent properties of concreteat early ages, was successfully performed to interpret the test results.